The present invention relates to monolithic integrated circuits. More particularly, it relates to monolithic integrated circuits for use in microwave applications.
The term monolithic integrated circuit generally refers to an integrated circuit in which substantially all active, passive and interconnection elements are disposed on a single substrate. When the circuit incorporates a power semiconductor device such as an amplifier, the circuit is typically bonded to a heat sink and includes some form of electrical passivation such as hermetic sealing within a device package.
Monolithic integrated circuits for use at microwave frequencies are typically ormed in compound semiconductors such as semi-insulating GaAs and typically incorporate a microstrip circuit pattern on a major substrate surface. As with integrated circuits generally, the design of monolithic microwave integrated circuits for power applications requires certain tradeoffs. For example, while a relatively thin substrate might be desirable from the standpoint of heat dissipation, a thin substrate will increase the extent of circuit losses (Q) of a microstrip circuit disposed on the substrate. A conventional device/heat sink configuration, utilizing a contact plated through the substrate, is disclosed in U.S. Pat. No. 3,986,196, THROUGH-SUBSTRATE SOURCE CONTACT FOR MICROWAVE FET, issued Oct. 12, 1976 to D. R. Decker et al. A conventional monolithic microwave integrated circuit, incorporating an FET and a microstrip circuit on the same substrate, is disclosed in the article AN X-BAND GaAs FET MONOLITHIC POWER AMPLIFIER, by R. A. Pucel et al, published in the 1979 International Microwave Symposium Digest, Apr. 30-May 2, 1979.